The present invention falls within the field of devices for mounting the rails of a railway track. It relates more particularly to a track support system to be affixed directly onto a bed or floor or onto sleepers.
Current devices for fixing track rails include fastener means and at least one pad made of elastic material which gives elasticity to the wheel-rail assembly so that there is obtained a degree of is of the environment with respect to the vibrations produced by the dynamic forces applied to the rails when a vehicle runs on the rails.
There is almost always an elastic device in the form of a relatively rigid pad directly beneath the rail. There is often a second, more flexible pad beneath a metal sole-plate or a sleeper. The latter pad provides anti-vibration isolation.
The first resonant frequency, in flexure, of the wheel-rail assembly depends on the dynamic stiffness of the pads. This resonant frequency is inversely proportional to the anti-vibration performance of the rail-fixing system: a low resonant frequency gives better anti-vibration isolation than a high resonant frequency. With pads which have a low dynamic stiffness, the first resonant frequency of the wheel-rail assembly is reduced, thereby giving rise to a good anti-vibration filter. The best filter is therefore obtained with the lowest dynamic stiffness of the pads.
However, there is a lower physical limit to this dynamic stiffness of the pads used in the current rail-fixing systems. The dynamic stiffness is directly proportional to the static stiffness of the pads. The static stiffness of the pads cannot be too low because of the fact that it has a direct influence on the deflection of the rails when a vehicle is running along the rails. This rail deflection is generally limited to approximately 3 mm. This static rail deflection limit imposes a minimum static stiffness, and thus a minimum dynamic stiffness of the anti-vibration pad. This phenomenon limits the anti-vibration isolation performance of the current rail-fixing systems. For most current fixing devices, the resonant frequency lies between 35 Hz and 60 Hz.
In order to obtain a superior isolation performance to that obtained with the current fixing systems, it is necessary for the fixing and isolation functions to be completely decoupled. This is realized in systems of the floating-slab type in which the rails are fixed onto a slab which is itself isolated from the environment by anti-vibration studs placed between the slab and the bed (or floor). In the case of a floating slab, the resonant frequency lies between approximately 10 Hz and 25 Hz, which gives a better anti-vibration filter. The latter systems are however very expensive and difficult to maintain.